Temperature stability and electrical properties in La‐doped KNN‐based ceramics

• Published in: Journal of the American Ceramic Society 2018-09, Vol.101 (9), p.4084-4094
• Main Authors: Lv, Xiang, Wu, Jiagang, Zhu, Jianguo, Xiao, Dingquan, Zhang, Xi‐xiang
• Format: Article
• Language: English
• Subjects: Ceramics; Curie temperature; Electrical properties; KNN ceramics; lanthanum; lead‐free; Phase boundaries; Phase transitions; Piezoelectricity; Rare earth elements; Solid phases; Temperature effects; temperature stability
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/jace.15695

To improve the temperature stability and electrical properties of KNN‐based ceramics, we simultaneously consider the phase boundary and the addition of rare earth element (La), 0.96K0.5Na0.5Nb0.96Sb0.04O3‐0.04(Bi1‐xLax)0.5Na0.5ZrO3 (0 ≤ x ≤ 1.0) ceramics. More specifically, we investigate how the phase boundary and the addition of La3+ affect the phase structure, electrical properties, and temperature stability of the ceramic. We show that increasing the La3+ content leads to a change in phase structure, from a rhombohedral‐tetragonal (R‐T) phase coexistence to a cubic phase. More importantly, we show that the appropriate addition of La3+ (x = 0.2) can simultaneously improve the unipolar strain (from 0.127% to 0.147%) and the temperature stability (i.e., the unipolar strain of 0.147% remains unchanged when T is increased from 25 to 80°C). In addition, we find that the ceramics with x = 0.2 exhibit a large piezoelectric constant (d33) of ~430 pC/N, a high Curie temperature (TC) of ~240°C and a fatigue‐free behavior (after 106 electric cycles). The enhanced electrical properties mostly originate from the easy domain switching, whereas the improved temperature stability can be attributed to the R‐T phase boundary and the appropriate addition of La3+.